FIG. 1 is a diagram useful in describing a technique for calibrating a color printer.
As shown in FIG. 1, an ink color decomposing processor 901 decomposes multivalued RGB image data, which is input thereto, into data of the color components C (cyan), M (magenta), Y (yellow) and K (black) corresponding to the colors of the colorants (referred to as “ink colors” below) of the color printer by interpolation processing such as tetrahedral interpolation based upon table information in an ink color decomposition table 907.
A one-dimensional LUT 902 for calibration purposes corrects the grayscale characteristic of the image data in accordance with the color reproduction characteristic of the printer. Specifically, the LUT 902 corrects the multivalued CMYK data that is output from the ink color decomposing processor 901 to multivalued C′M′Y′K′ data. A calibration conforming to the characteristic of the color printer is achieved by this processing.
A halftoning processor 903 converts the multivalued C′M′Y′K′ data to a number of tones capable of being printed by the color printer. If the color printer is, e.g., a binary printer, then the C′M′Y′K′ data is binarized by the halftoning processing, whereby the processor 903 outputs binary C″M″Y″K″ data.
A color printer engine 904 performs printing based upon the C″M″Y″K″ data input thereto.
A sensor 906 investigates the color reproduction characteristic of the color printer engine 904. On the basis of the color reproduction characteristic of each of the colors CMYK output from the sensor 906, a one-dimensional LUT creating unit 905 creates a one-dimensional LUT of each of the colors CMYK in such a manner that a target color reproduction characteristic will be obtained. The result of this operation is written to the one-dimensional LUT 902.
The technique using the one-dimensional LUT 902 shown in FIG. 1 calibrates each of the colors CMYK independently and therefore implements a highly accurate calibration with regard to first-order colors (ink colors). However, a highly accurate calibration cannot be achieved with regard to colors other than first-order colors, such as the second-order colors R (red), G (green) and B (blue), and the third- and fourth-order colors, which form a gray line.
A method of calibrating second- and higher-order colors by reconstructing the content of the ink color decomposition table 907 is available as a method calibrating second-, third- and fourth-order colors, etc. However, it is difficult to reconstruct the ink color decomposition table 907 while maintaining a limitation upon the overall amount of ink allowed by the printing paper.
Furthermore, since the latest ink-jet printers employ a six-color ink system that uses light cyan and light magenta in addition to cyan, magenta, yellow and black (the conventional first-order colors) as the ink colors, it is even more difficult to maintain the above-mentioned limitation. The same holds true for other printers such as electrophotographic printers as well.